Various types of devices configured to conduct engine sound from the engine compartment of a motor vehicle into the passenger compartment are known. As engine designs evolve for great fuel efficiency, current varieties of motor vehicles have internal combustion engines that operate very smoothly so that the engine operating sound may be barely audible within the interior of the motor vehicle. A further reduction in engine sound may result from noise dampening foams and acoustic insulation arranged to limit the migration of road noise into the passenger compartment. The use of turbocharged engines have also caused the natural sounds of the engine to be masked by noise coming from the turbo which are high pitched and unpleasant. Additionally the engine operating sound level may become further obscured by the presence of other secondary noises such as vehicle HVAC systems, etc.
Drivers operating certain classes of sporty or higher performance vehicles appreciate and may come to expect the presence of a sporty, rumbling or throaty engine sound that is on par with the power and performance of the vehicle. The sound character from the vehicle is also a brand image directed to differentiate one particular brand from another. Given the deficiency of a suitable engine sound level in some vehicle, a need exists to restore the throaty, sporty engine sound experience to enhance the driving experience of the vehicle operator.
To remedy such deficiencies it can be desirable to provide an enhanced transmission of the engine operating sound to the interior of the motor vehicle. Suitable sound energy levels are often present in the engine air intake tract if a suitable means to direct this sound energy into the vehicle interior is provided.
It is known to provide a sound transmission tube having a sound-transmitting diaphragm, with the sound transmission tube originating at a sound pickup point near the engine (such as the air intake tract), and routed towards or into the passenger compartment. In such sound transmission devices the flexible diaphragm is installed into the sound transmission tube to provide airflow isolation while permitting the transmission of sound through the diaphragm. Use of an elastomeric diaphragm such as a rubber diaphragm is useful to provide this airflow impermeable separation between the passenger compartment interior and the sound pickup in the engine compartment. Unfortunately, such elastomeric diaphragms may also introduce frequency dependent distortions in the sound level and sound quality transmitted into the passenger compartment and experienced by the driver.
It is known to provide tuning of a transmitted sound spectrum in a vehicle sound transmission device by the addition of a quarter wave tuner or a resonator chamber installed inline with the sound transmission tubing. A quarter wave tuner is useful to attenuate or cancel a selected transmitted sound frequency. The quarter wave tuner may be positioned and connected to the sound transmission tubing so as to extend outwards from the tubing in a branch configuration, typically (although not necessarily) at about 90 degrees relative to the axis of the sound transmission tubing. Alternately, when it is desired to amplify a selected transmitted sound frequency, then an inline resonator chamber may be provided in the sound transmission tubing. If the inline resonator is configured with a duct length L, then the amplified sound wavelength will be a function of L/2. The use of quarter wave tuners and inline resonators, alone or in combination, permit the transmitted sound to be tailored using only passive devices rather than by the application of more expensive and complicated active electronic devices.
U.S. published patent application 2009/0250290A1 discloses a device for noise transmission in a motor vehicle. In this device sound is transmitted along a transmission line having an enlarged mouth at one end and an elastomeric diaphragm fitted to close off the mouth. A protective device is fitted at the end to protect the diaphragm, such as from overpressure conditions.
U.S. Pat. No. 6,600,408 B1 discloses a diaphragm device for sound transmission for a motor vehicle. In this device, the sound is transmitted along a pipe conduit and a chamber in which an elastomeric diaphragm sealably closes the end of the pipe conduit to airflow. The diaphragm closed end is arranged toward the interior of the motor vehicle. The chamber that surrounds the diaphragm is comprised of several assembled parts.
German patent publication DE 101 16 169 A1 discloses a resonator chamber in which the diaphragm is arranged.
German patent DE 44 35 296 discloses a diaphragm for noise transmission in a motor vehicle in which the diaphragm is clamped in a holder.
U.S. published patent application 2006/0283658 A1 discloses another diaphragm based noise transmission system for an intake system of a motor vehicle. Various possibilities of noise introduction into the interior of the motor vehicle are illustrated wherein the diaphragm is arranged in a pipe conduit for noise transmission.
In the German publication DE 199 30 025 A1 a sound transmission body is illustrated in which the diaphragm is clamped between two transmission members.
There remains a need in the art for a device to transmit a suitable level of engine sound into the vehicle passenger compartment that is simple in construction and eliminates the issues of detuning and distortion of the transmitted sound, particularly by a diaphragm sound transmission device.